Apparatus for protection of rotor vanes against surface erosion caused by impingement of high speed liquid drops

ABSTRACT

The surface of a structural part such as for example the leading edge portion of a turbine vane or airplane wing is protected against erosion which would otherwise be caused by impingement of high speed liquid drops thereon by positioning an array of flexible baffles in front of the surface. These baffles which are slightly spaced from the surface of the vane or wing serve to intercept the liquid drops resulting in a division thereof into smaller drops which are simultaneously decelerated as a result of flexation of the baffles.

United States Patent Faber et al.

[ Sept. 5, 1972 [54] APPARATUS FOR PROTECTION OF ROTOR VANES AGAINSTSURFACE EROSION CAUSED BY IMPINGEMENT OF HIGH SPEED LIQUID DROPS [72]Inventors: Guy Faber, Oberrohrdorf; Carlo Maggi, Baden, both ofSwitzerland [73] Assignee: Aktiengesellschaft Brown, Boveri 8:

Cie, Baden, Switzerland 22 Filed: Nov. 23, 1970 [21] Appl.No.: 91,869

[30] Foreign Application Priority Data Dec. 23, 1969 Switzerland..19070/69 [52] US. Cl ..416/224, 416/228 [51] 7 Int. Cl ..F01d 5/28[58] Field of Search ..416/62, 224, 228; 415/ 168 [56] References CitedUNITED STATES PATENTS 1,862,827 6/ l 932 Parsons et a1 ..416/2243,023,840 3/ 1962 Flamm ..416/224 X 3,347,520 10/ 1967 Onczarek..416/228 X 3,365,126 1/19 68 StOfier et al ..416/228 3,403,893 l0/ 1968Stoffer ..416/228 FOREIGN PATENTS OR APPLICATIONS 311,010 2/1919 Germany..416/224 233,693 7/1969 U.S.S.R. ..416/224 Primary Examiner-Everette A.Powell, Jr. AttorneyPierce, Scheffler & Parker [57] ABSTRACT The surfaceof a structural part such as for example the leading edge portion of aturbine vane or airplane wing is protected against erosion which wouldotherwise be caused by impingement of high speed liquid drops thereon bypositioning an array of flexible baffles in front of the surface. Thesebaffles which areslightly spaced from the surface of the vane or wingserve to intercept the liquid drops resulting in a division thereof intosmaller drops which are simultaneously decelerated as a result offlexation of the bafiles.

4 Claims, 3 Drawing Figures PATENTEDSEF 5 I912 3.6891 18 603 Faber CarloM613 1;

3% law a fivkgglawmfww APPARATUS FOR PROTECTION OF ROTOR VANES AGAINSTSURFACE EROSION CAUSED BY IMPINGEMENT OF HIGH SPEED LIQUID DROPS Thisinvention relates to an improved device for the protection of the vanesof a rotor against erosion which are imperiled by liquid drops impingingthereon at high speed.

When liquid drops impinge on metals or other materials at very highspeeds, they cause erosion, that is, small particles of material breakoff after a certain time. The erosion effect depends mainly on the speedof impingement of the drops, their diameter, the angle of incidence onthe surface of the structural part, and the specific properties of theeroding material. Due to the removal, the surface first becomes rough,then peaks opposed to the impinging drops form, which are now removedmore slowly but continue to be removed. The friction losses of a flowalong such eroded surfaces are correspondingly great.

Low pressure vanes on steam turbines, running temporarily or permanentlyin the saturated steam zone, are very susceptible to erosion. Especiallythe radially external portion of the entrance edge may be erodedintensively, and this leads to a loss of efficiency. It should be takeninto consideration also that eroded vanes can hardly be repaired.

For protection against erosion, therefore, steam turbine vanes areproduced either of an erosionproof 3O of stellite shields involvesdifiiculties in the case of titanium vanes because of the temperatureinfluences during brazing, and in the case of plastic vanes because ofthe weight. Also, in the case of stellites, the properties of a materialdeterminant for the erosion resistance, namely strength combined withtoughness, can hardly be increased any further, so that at increasedcircumferential speeds greater erosions are to be expected even withstellites.

When airplanes fly through rain clouds at supersonic speed, the wingnoses are so intensively eroded by the rain drops that already afterseveral times the planking consisting of a light metal alloy must beexchanged. The only remedy is seen in increasing the erosion resistanceof the metals used.

The principal object underlying the present invention is to protectagainst the erosion of structural parts endangered by drop impactwithout having to subject the material to a special treatment andwithout having to replace it in the specially affected areas by a moreerosion-resistant material.

This problem is solved according to the invention in that the drops aredivided and, at the same time, decelerated before they impinge on thestructural parts.

A device for carrying out this method is characterized by baffle bodiesof small mass which are arranged, viewed in the direction of incidenceof the drops, ahead of the endangered structural parts.

Instead of a fixed, stifi, solid erosion shield, there are used,according to the invention, baffle bodies which, due to their smallmass, and because they do not rest on anything except for theirattachment to the structural part to be protected, are flexible andhence can be elastically deflected in the direction of incidence orlaterally thereto when a drop impinges. This yielding of the bafflebodies upon impingement of a drop gives the same effect as a lowerimpingement speed. Due to the narrow and usually also curved impingementsurface offered to the drops, the angle of incidence is more favorablethan in the case of impingement normal to the impingement surface. Thedrops are divided and so slowed in their velocity that the erosioneffect on the imperiled structural parts behind the baffle bodies isgreatly reduced. Y

If thesestructural parts are, for example, the impellers of alow-pressure turbine, running in the saturated steam zone, they can beprotected by preceding fixed baffle bodies installed in the flow path,e.g. a wire mesh. However, the effect is greater if the baffle bodiesco-rotate in the same direction of rotation as the vanes, preferably atthe same speed. They may be fastened either to the rotor or to the vanesthemselves. As the vanes are endangered by drop impact mainly toward thetip, it may sometimes be sufficient to protect only their radiallyexternal portion. The stress of the baffle bodies caused by thecentrifugal force is thereby greatly reduced; yet it is advantageous totaper them conically in radial direction outwardly.

The drops impinge close to the stagnation or ram point of the profile,and therefore, if the baffle bodies are fastened on the rotor or on thevanes, they are provided only in this region. Also it is not necessaryto protect each vane separately, as five or six vanes are coveredtogether and are sufficiently protected by baffle bodies mounted infront.

The baffle bodies may be made, for example, of colddrawnstainless steel.Experiments have shown that the erosion effect greatly decreases withdecreasing wire diameter. A thickness of the baffle bodies of 1 mm is tobe regarded practically as the upper limit. A few millimeters distanceof the baffle bodies from the imperiled structural parts are sufficientfor adequate protection.

Two examples of construction of the invention are illustrated insimplified form in the accompanying drawings, wherein:

FIG. 1 shows a steam turbine vane in front view;

FIG. 2, a single baffle body on a larger scale; and

FIG. 3, an airplane wing in partial view.

According to FIG. 1, the entrance edge of the turbine vane 1 isprotected at its radially external portion by wires 2, which are securedto the ribs 3,4. They extend at a small distance from the vaneapproximately parallel with one another. Because of the high stressexerted by the centrifugal forces, a careful attachment to the ribs 3 isnecessary.

An example of this is illustrated in FIG. 2. It shows a single wire 2greatly enlarged, especially the thickness being much exaggerated. Theoutwardly tapering wire is welded into the rib 3, while at rib 4 it isfastened only by spot welding, because there only relatively smallforces must be absorbed. According to the occurring stress, the wire mayalternatively be jointed to the ribs by brazing or otherwise.

Instead of providing the rib 3, the profile may be recessed at thispoint, the wires extending in the original profile line, whereby thenecessary spacing and the desired flexibility are established. Also, thewires may extend over the full length of the vane blade and may be held,for example, in a bottom plate, which is fastened to the root of thevane. Another possibility, already mentioned, consists in fastening thewires directly to the rotor, that is, in front of the vane root.

FIG. 3 shows another possible use of the baffle bodies. Before the noseof an airplane wing 5 a wire grid 6 is applied, which protects theplanking against impinging rain drops.

Other uses of the baffle bodies are conceivable wherever high speedsoccur, especially greater than Mach 1, and liquid drops are contained inthe gaseous medium. Exchangeability of the baffle bodies is of advantagein most cases.

We claim:

1. A device for protecting the vanes of a rotor against surface erosioncaused by impingement of liquid drops thereon at high speed whichcomprises an array of thin flexible baffles positioned in front of andspaced from the surface of each vane, said baffles serving to interceptand decelerate the droplets prior to striking the vane surface as aresult of flexation of said baffles, and said baffles also serving todivide the droplets into smaller masses, thereby to reduce their impactforce upon the vane surface. I

v 2. A device as definedin claim 1 for protecting the vanes of a rotoragainst surface erosion wherein said baffles are constituted by an arrayof parallel spaced thin flexible wires enveloping the leading edgeportion of the vane and extending in a radially outward direction, saidwires being spaced from the vane surface and being secured thereto onlyat their ends.

3; A device as defined in claim 2 for protecting the vanes of a rotoragainst surface erosion wherein said wires are tapered in the radiallyoutward direction.

4. A device as defined in claim 1 for protecting the vanesof arotor-against surface erosion wherein said baffles are constituted bythe wires of a thin flexible wire grid, said grid enveloping the leadingedge portion of the vane and being secured thereto in spaced relation.

i t t i

1. A device for protecting the vanes of a rotor against surface erosioncaused by impingement of liquid drops thereon at high speed whichcomprises an array of thin flexible baffles positioned in front of andspaced from the surface of each vane, said baffles serving to interceptand decelerate the droplets prior to striking the vane surface as aresult of flexation of said baffles, and said baffles also serving todivide the droplets into smaller masses, thereby to reduce their impactforce upon the vane surface.
 2. A device as defined in claim 1 forprotecting the vanes of a rotor against surface erosion wherein saidbaffles are constituted by an array of parallel spaced thin flexiblewires enveloping the leading edge portion of the vane and extending in aradially outward direction, said wires being spaced from the vanesurface and being secured thereto only at their ends.
 3. A device asdefined in claim 2 for protecting the vanes of a rotor against surfaceerosion wherein said wires are tapered in the radially outwarddirection.
 4. A device as defined in claim 1 for protecting the vanes ofa rotor against surface erosion wherein said baffles are constituted bythe wires of a thin flexible wire grid, said grid enveloping the leadingedge portion of the vane and being secured thereto in spaced relation.